The present invention relates to the field of measurement systems and, in particular, to an apparatus and method for in-process measurement, control and recordkeeping for the manufacture of uniform kerfs, slots or grooves in thick materials, created during material processing.
In making cardboard boxes, a wooden die is prepared that is used to crease and cut the cardboard so that it is shaped and subsequently folded accurately. A kerf or narrow groove is made in the plywood that serves to diagonally hold thin steel strips or rule that imprint the cut and fold lines on the cardboard when the die is placed in a press. If the kerf is not accurately cut, the steel rule strips will not be held tightly in the die or will not be in the right position and the cardboard will not be creased or cut properly. This problem is exacerbated by the fact that the wooden dies are often very large.
The laser has long been used for cutting the knifing grooves in flat and rotary dieboards. For many years the technology was limited to the use of 500 watt CO2 lasers with fixed distances from the laser to the focusing lens to cut plywood into desired shapes for use as dieboards. The key processing parameters were the control of the top and bottom kerf dimensions, kerf verticality or perpendicularity to the board surface, and kerf walls that remained within known tolerances of being straight.
From the nature of the laser cutting process, the dieboards were placed on an open faced enclosure or xe2x80x9ctubxe2x80x9d which would catch scrap material, collect the smoke and fumes for proper exhaust, and provide for safety by eliminating the exposure of the operators to laser radiation. As a consequence of this construction, the bottom of the dieboard is not accessible to the operator during the cutting process, and a xe2x80x9cdirectxe2x80x9d measurement of the bottom kerf width is not possible. Operators check the top kerf width using a taper gauge and use an indirect procedure for determining the correctness of the bottom kerf width dimension by inserting a blade or xe2x80x9crulexe2x80x9d into the kerf and xe2x80x9cfeelingxe2x80x9d the resistance to insertion and withdrawal. This is a subjective procedure depending on the instincts of the operator. Often this procedure is repeated several times during the cutting process.
As technology has advanced to higher power lasers and moving optic systems, cutting speed has increased dramatically, and this increase in speed makes it more difficult to control the key process parameters. It is not recognized in the prior art nor has anyone provided a reliable method for determining the bottom kerf width while cutting as this would allow in-process adjustments to be made to key parameters thus producing the highest possible of quality throughput. While the top kerf width is more predictable and readily controlled by focusing techniques, the bottom kerf width is dependent on a xe2x80x9cburningxe2x80x9d process which can be affected by a number of variables inherent in the plywood being cut, the laser, the motion system, the process environment and system programming.
In current practice, test cuts are made in the plywood in the X and Y directions and checked by inserting a taper gauge or a piece rule to measure the top and bottom kerf width as described above. Laser and motion system parameters are consequently adjusted and additional test cuts are made until the estimated top and bottom widths are correct. Once actual cuts are made in the workpiece, the dimensions may or may not be periodically checked in a similar fashion over the entire board length depending upon its size, material, required accuracy, and operator sensitivity.
As is apparent from the above description, the current measuring process is imprecise and during cutting depends on the subjective actions of the operator. The final product can only be measured in total after the material is fully cut. If there are kerf width problems, the result is increased scrap and wasted machine and operator time down time. Once the dieboard has been cut, the offline measurement of the plywood will require the use of a separate machine measurement system where the kerfs on each side can be viewed accurately by an experienced operator. This secondary operation substantially increased the cost of the product.
Another measuring process that has been proposed in the art is a machine vision system for in-process kerf measurement. This system employs a camera mounted coaxially to the laser cutting beam. The camera is offset from the cutting beam in order to get a clear view of the cut slot after the laser burn residue is eliminated. However, this system has many drawbacks. First, the machine vision system does not provide a direct measurement of the kerf width from the bottom of the dieboard. Second, the quality of the measurement of the bottom kerf is limited by the clarity of the field of view due to the unpredictable nature of the residue exhaust. Finally, the data processing requirements, for processing and analyzing the camera image, is very time consuming and therefore not practical for efficient dieboard processing.
Therefore, there is a need for a system for measuring the kerf of the laser cut plywood dieboard which provides accurate, digital and automatic in-process measurement of the entire kerf, on the bottom as well as the top of the dieboard, thereby making it possible to adjust system variables during the cutting process so that both scrap and machine/operator down-time are reduced.
In accordance with one aspect of the present invention, an in-process kerf measuring device for measuring a kerf made from a cutting device. The device includes a taper gauge having a top and bottom, the taper gauge being a predetermined shape and size and capable of being inserted into or probing the kerf. The device also includes a spring coiled around the taper gauge, a shaft having a top and a bottom, the top of the shaft is in mating relation to the bottom of the taper gauge, an outer gauge housing that serves to vertically align, contain and provide stability to the taper gauge, spring and shaft, a horizontal plate having a resting position, the bottom of the shaft is vertically retained and rotatably attached to the horizontal plate. The device also includes a stroke means, where the stroke means is in connected relation to the horizontal plate, a measurement means for measuring the kerf and a means for actuation of the device. In practice, the device works as follows: the means for actuation rotates the device planar to the X or Y direction kerf. The device is in the measurement means starting position. The stroke means than thrusts the horizontal plate upward, thrusting the shaft, taper gauge and outer gauge housing upward which after contacting the flat surface of the workpiece acts to compress the spring. This then causes the top or narrowest end of the taper gauge to extend further, probing the kerf until reaching a stopping position. At that stopping point, the measurement means measures the kerf using data collected from the starting position and the stopping position.
Implementation of this aspect of the present invention may include one or more of the following. The stroke means is a linear air or fluid cylinder, the apparatus measuring means is a rotary encoder, the means for actuation is a rotary vane air cylinder, the means for actuation is a stepper motor, the apparatus measuring means is a linear digital encoder.
In accordance with another aspect of the invention, a method for in-process kerf measuring for measuring a kerf made from a cutting device. The method includes a first step of rotating a kerf measuring device to a starting position, where the device includes a taper gauge having a top and bottom, the taper gauge being a predetermined shape and size and capable of probing the kerf. The device also includes a spring coiled around the taper gauge, a shaft having a top and a bottom, the top of the shaft is in mating relation to the bottom of the taper gauge, an outer gauge housing that vertically aligns and contains the taper gauge, spring and shaft, a horizontal plate having a resting position, the bottom of the shaft is slidably attached to the horizontal plate. The device also includes a stroke means, where the stroke means is in connected relation to the horizontal plate, a measurement means for measuring the kerf and a means for rotation of the device. The method also includes a second stop of thrusting the horizontal plate upward, a third step of thrusting the shaft, taper gauge, spring and gauge housing upward, a fourth step of contacting the flat surface of the workpiece, a fifth step of compressing the spring, a sixth step of probing the kerf with the taper gauge until reaching a stopping position, and a final step of returning to said starting position.
Implementation of this aspect of the present invention may include one or more of the following. The stroke means is a linear air or fluid cylinder, the apparatus measuring means is a rotary encoder, the means for actuation is a rotary vane air cylinder, the means for actuation is a stepper motor, the apparatus measuring means is a linear digital encoder.